1. Field of the Invention
The present invention relates to a composite hose with a corrugated metal tube, which is suitable for a fuel transporting hose for a motor vehicle or a hose transporting fluid such as refrigerant, and more particularly to a composite hose with a corrugated metal tube having a specific fastening structure on an end portion thereof.
2. Description of the Related Art
Typical rubber hoses, for example, made of blended product of acrylonitrile-butadiene rubber and polyvinyl chloride (NBR/PVC blend) that is excellent in a gasoline permeation resistance, have been used for conveying fuel for automobiles or the like in view of their high vibration-absorbability, easiness of assembly or the like. However, for the purpose of global environment protection, the regulations have been recently tighten against permeation of a fuel for motor vehicles or the like, and are anticipated to be further tightened in the future. Further, on the other hand, hoses are demanded to meet the requirements to convey highly permeable fluid such as hydrogen gas used in fuel cells or carbon dioxide (CO2) refrigerant. Then it is anticipated difficult to satisfy the future requirements with hoses made only of organic materials such as rubber or resin.
Accordingly, it is currently considered to adapt a hose with a corrugated metal tube that defines an inner layer for which extremely high fluid impermeability is expected for future application of a fluid impermeable hose.
In case of the composite hose with the corrugated metal tube, even when adapted for hydrogen gas of small molecular mass used for fuel cells, a corrugated metal tube as the inner layer reduces gas permeation zero, i.e., completely eliminates permeation of gas.
However, as an inner layer, i.e., a corrugated metal tube in the hose with the corrugated metal tube is difficult to deform, if the hose with corrugated metal tube is adapted, it will be a problem how to construct fastening structure on an end portion of the hose with the corrugated metal tube so as to assure sealing property thereon.
Conventionally, as shown in FIG. 7, fastening structure for an end portion of typical rubber hose is constructed in a following manner. First, a rigid metal inert pipe 202 is inserted in a hose body 200, a socket fitting 204 including a radially inwardly directed collar portion 206 is fitted on the hose body 200. And then, the socket fitting 204 is swaged radially inwardly onto the hose body 200. The hose body 200, the insert pipe 202 and the socket fitting 204 are securely fastened in unitary relation with one another by swaging the socket fitting 204 radially inwardly onto the hose body 200 and a seal is thereby provided between an inner surface of the hose body 200 and the insert pipe 202.
However, in the composite hose with the corrugated metal tube, it is hard to bring about a sufficient bonding strength between the corrugated metal tube and the insert pipe. When a seal is provided only by fitting relation between the inner circumferential surface of the corrugated metal tube and the outer circumferential surface of the insert pipe, it is difficult to ensure sufficient sealing property therebetween.
In order to solve this problem, the inventor (the applicant) devised a following composite hose with a corrugated metal tube. In this composite hose, a hose body is constructed by laminating an outer layer including an elastic layer on an outer side of a corrugated metal tube as an inner layer. The corrugated metal tube has a non-corrugated straight-walled portion of a straight tubular shape extending straight in an axial direction on an end portion thereof, and an end part of the straight-walled portion extends axially outward from the outer layer to define an extending portion. And, a rigid insert pipe is inserted in the straight-walled portion in the hose body, and a sleeve-shaped socket fitting is fitted on the hose body and swaged thereon radially inwardly. The socket fitting includes a radially inwardly directed collar portion, and an annular fit-in groove is formed in an outer circumferential surface of the insert pipe. The socket fitting is swaged on the hose body in a manner such that an inner circumferential end or an inner circumferential end portion of the collar portion of the socket fitting is fitted in and engaged with the fit-in groove with plastic deformation while force-fitting the extending portion into the fit-in groove. And, the collar portion or a fit-in portion of the collar portion and the fit-in groove sandwich and compress a force-fitted portion of the straight-walled portion therebetween to provide a seal between the straight-walled portion and the insert pipe and fix the straight-walled portion to the insert pipe. This composite hose with the corrugated metal tube is disclosed in the previous patent application (Patent Document 1 below).
FIG. 8 shows concretely the composite hose according to this patent application.
In the Figure, reference numeral 200 indicates a hose body that has a multilayer construction. The hose body 200 comprises an innermost layer constructed by a corrugated metal tube 204, and an outer layer laminated on an outer side of the corrugated metal tube 204 and constructed by an inner elastic layer 206, a reinforcing layer 208 and an outer elastic layer 210, and these layers are securely bonded each other in unitary relation.
The corrugated metal tube 204 has a corrugated portion 212 generally along an entire length thereof, and is provided with flexibility by the corrugated portion 212.
The corrugated metal tube 204 has a non-corrugated straight-walled portion 214 of a straight tubular shape on an end portion thereof, and the straight-walled portion 214 extends straight continuously from the corrugated portion 212 in an axial direction.
Here, an end part of the straight-walled portion 214 extends axially outwardly so as to be exposed out of the outer layer to define an extending portion that is indicated at reference numeral 216 in the Figure.
Reference numeral 222 indicates a rigid insert pipe (made of a metal here) and reference numeral 218 indicates a sleeve-shaped socket fitting. The socket fitting 218 has a radially inwardly directed collar portion 220 on an axial end portion thereof.
Here, an inner diameter of the above straight-walled portion 214 is set equal to an outer diameter of the insert pipe 222 in view of facilitating assembly of the hose body 200 and the insert pipe 222.
FIG. 8 (A) shows a state before the socket fitting 218 is swaged on the hose body 200.
As shown in the Figure, in this composite hose with the corrugated metal tube, the insert pipe 222 is inserted in the straight-walled portion 214 of the corrugated metal tube 204, the socket fitting 218 is fitted on the hose body 200, the socket fitting 218 is swaged onto the hose body 200 radially inwardly to fasten an end portion of the hose body 200, the insert pipe 222 and the socket fitting 218 together in unitary relation.
By swaging the socket fitting 218 onto the hose body 200, as shown in FIG. 8 (B), the extending portion 216 of the straight-walled portion 214 is sandwiched and compressed by and between an inner circumferential end of the collar portion 220 and an outer circumferential surface of the insert pipe 222 to perform two functions at a time, namely to fix the straight-walled portion 214 to the insert pipe 222 and to provide a seal therebetween.
In particular, in this prior art example, an annular fit-in groove 213 is formed in the outer circumferential surface of the insert pipe 222 corresponding to the collar portion 220, when the socket fitting 218 is swaged onto the hose body 200, an inner circumferential end portion of the collar portion 220 is fitted in the fit-in groove 213 while being plastically deformed by the fit-in groove 213 to define a fit-in portion 221 (refer to a fragmentary enlarged view of FIG. 8B) of a shape following a contour of the fit-in groove 213. The fit-in portion 221 and the fit-in groove 213 are fitted each other via the extending portion 216 that is deformed so as to enter in the fit-in groove 213, thereby fixing the straight-walled portion 214 to the inert pipe 222 and providing a seal between the insert pipe 222 and the straight-walled portion 214.
Meanwhile, as shown in FIG. 8B, here, the socket fitting 218 is swaged at a plurality of swaged positions in an axial direction thereof. Specifically, the socket fitting 218 is swaged radially inwardly at each of a plurality of swaged positions, P1, P2, P3 and P4 in the axial direction thereof.
However, later on, a problem is found that a durability or durable life of the straight-walled portion 214 is not sufficient in the composite hose with the corrugated metal tube.
Specifically, a durability test was conducted with the composite hose with the corrugated metal tube by exerting an internal pressure to the composite hose repeatedly, and the problem is found that an axial fracture or axial crack was caused on a part of the straight-walled portion 214.
Then, the inventor studied the cause of the fracture and found out the fact as follows.
In the composite hose with the corrugated metal tube, the collar portion 220 of the socket fitting 218 and the outer circumferential surface of the insert pipe 222 sandwich and compress the extending portion 216 therebetween to provide a seal therebetween. However, on a portion of the straight-walled portion 214 extending to the right with respect to the collar portion 220in the Figure, the bonding strength is small, for example, a clearance (gap) is created between the inner circumferential surface of the straight walled portion 214 and the outer circumferential surface of the insert pipe 222. Due to that, when an inner pressure is exerted to the composite hose with the corrugated metal tube, an internal fluid enters between the inner circumferential surface of the straight-walled portion 214 and the outer circumferential surface of the insert pipe 222, and the internal pressure is exerted also to the straight-walled portion 214 repeatedly. As a result, a region of the straight-walled portion 214 is expansively and contractively deformed in a radial direction repeatedly. Then, the inventor reached the conclusion that this repeated expansive and contractive deformation caused a metal fatigue in this region of the straight-walled portion 214, and an axial fracture was caused in the deformed region of the straight-walled portion 214.
And, at the same time, it was found that an axial fracture is liable to occur in a region between one and adjacent swaged portions of the socket fitting 218.
The cause of this fracture or phenomenon may be estimated as follows.
When the socket fitting 218 is swaged at positions of P1, P2, P3 and P4, the outer elastic layer 210 is deformed so as to escape or enter into a recessed portion 224 between the swaged positions inside the socket fitting 218, namely a large volume displacement was caused.
At that time, the straight-walled portion 214 is also pushed in an axial direction due to movement of the reinforcing layer 208 and the inner elastic layer 206 accompanying movement of the outer elastic layer 210, and a region between the swaged positions in the straight-walled portion 214 is expansively deformed radially outwardly so as to have a wave pattern as shown in FIG. 9.
This region with the wave pattern is vulnerable to a load or pressure from the internal fluid. As a result, the region is more expansively and contractively deformed repeatedly due to repeated cycling of the pressure from the internal fluid. Then, it is estimated that large local distortion and elongation is caused in the region, and finally, a fracture or crack propagates through the region in the axial direction due to metal fatigue.
In a fragmentary enlarged view of FIG. 8(A), reference numeral 213a indicated a bottom surface of the fit-in groove 213, and reference numeral 213b indicates a side wall of the fit-in groove 213 on a front side thereof, and reference numeral 213c indicates a side wall of the fit-in groove 213 on a rear side thereof.
The extending portion 216 is partly force-fitted in the fit-in groove 213 by being plastically deformed to define the force-fitted portion 226. The force-fitted portion 226 is sandwiched and firmly compressed between the bottom surface 213a and a pair of the side walls 213b, 213c of the fit-in groove 213, and the inner circumferential end surface, the axial outer surface on the front side and the axial inner surface on the rear side of the fit-in portion 221, which correspond to the bottom surface 213a and a pair of the side walls 213b, 213c of the fit-in groove 213, respectively. And, thereby the force-fitted portion 226 is fixed to the insert pipe 222.
By the way, in the composite hose with the corrugated metal tube, when the socket fitting 218 is swaged, the extending portion 216 of the straight-walled portion 214 is deformed while being elongated. Also, when a high internal pressure is exerted to an inside of the hose, the reinforcing layer 208 is pulled in the axial direction, a strong pull force acts axially on the straight-walled portion 214 in a part at a position of an opening corner portion 228 of the side wall 213c on the rear side shown in the fragmentary enlarged view of FIG. 10, and the straight-walled portion 214 is distorted and elongated largely locally at the part thereof.
And, when an elongated length resulted from distortion and elongation exceeds an elongation at fracture, the straight-walled portion 214 has a fracture in the part at the position of the corner portion 228. That problem is found later on.
Patent Documents 2 and 3 as well as Patent Document 1 disclose a technique such that a collar portion of a socket fitting and an outer circumferential surface of an insert pipe sandwich and compress a straight-walled portion of a corrugated metal tube, specifically an extending portion of the straight-walled portion therebetween radially to fix the straight-walled portion to the insert pipe and provide a seal between the straight-walled portion and the insert pipe.
[Patent Document 1] JP-A, 2004-52811
[Patent Document 2] JP-A, 2004-190702
[Patent Document 3] JP-A, 2004-190704
Under the circumstances stated above, it is an object of the present invention to provide a composite hose with a corrugated metal tube that can be restrained from fracture. According to one aspect of the present invention, it is an object to provide a composite hose with a corrugated metal tube that can be restrained from fatigue fracture and having an enhanced durable life. And, according to another aspect of the present invention, it is an object to provide a composite hose with a corrugated metal tube of which straight-walled portion can be favorably restrained from fracture at an opening corner portion of a fit-in groove, during swaging operation, or by strong pull-force exerted to a hose body when an internal pressure is exerted to the hose body.